The invention relates to rotatable chisel especially for mining machines, which is used mostly in conveying and cutting heads of cutter roller loaders. The rotating chisel comprises a shaft and a working part with a flange for support at the front of a chisel holder. And the end of the shaft part of the rotating chisel, an elastic friction ring is disposed. The friction ring is slipped onto a section, constructed for this purpose, of the chisel shaft, which is provided with an end flange. The end flange and the part of the shaft, constructed for accommodating the friction ring, protrude together with the friction ring partly over the edge of the chisel holder, in which the chisel is fastened.
Many solutions for constructing chisel shafts are known from the state of the art and depend upon the safety mechanism employed. The Polish patent application 316,848 discloses a chisel holder, which is widespread and has a wide flat groove in the vicinity of its end. When a chisel is inserted in the holder, an expansion sleeve, with surface elements constructed convexly at its surface, engages this groove and thus prevents the expulsion of the inserted chisel. In the case of this solution, the shaft of the chisel is completely in the chisel holder. It is a disadvantage of dissolution that the expansion sleeve, the so-called xe2x80x9cclip ringxe2x80x9d, is relaxed after insertion in the chisel holder. A gap therefore remains between its inside and the surface of the groove and the small particles of the rock, which have been removed, collect in this gap. As a result, the free rotatability of the chisel holder, which is important for uniform wear, is made difficult after a certain time. Because of the intercalated small particles, it is also difficult, if not impossible, to compress the expansion sleeve and, with that, to exchange and a worn out chisel. A similar construction of the chisel shaft is shown in the British patent 2146058 and the U.S. Pat. No. 4,484,783.
Further solutions for structural shapes of shafts and components of the safety mechanism are unknown from the U.S. Pat. No. 4,684,176. In an example (there FIG. 1), the shaft is short and inserted completely into a hole of the chisel holder. A friction expansion sleeve, made from a thin metal sheet, is used over the whole surface of the shaft from the end flange to the supporting flange. Such sleeves are also known from the Polish patent 173,146 or, for example, from the German patent 3,233,123. These solutions have the disadvantage that the insertion of the chisel in the chisel holder is made difficult, since the sleeve, in the relaxed state, has a diameter larger than that of the internal hole of the chisel holder. As the chisel is driven in, the sleeve therefore shifts to the upper, cylindrical part of the shaft up to the flange and prevents further insertion of the chisel into the hole or, in the reverse case, a knocking out of the whole. The leads to difficulties in underground working conditions.
There are similar problems with the chisel, which is disclosed in the EP 0 295 232 A1 and the sleeve of which also is in contact with the shaft over almost its whole length and, at the bottom, is buckled and engages a groove, and, at the top, is angled to the outside. As a result, when the chisel is inserted into the seat of the chisel holder, the sleeve once again is expanded and is pushed upward, which can lead to jamming.
In a different embodiment of the already mentioned U.S. Pat. No. 4,684,176 (FIG. 3), there is a construction, for which the shaft of the chisel is longer than the hole of the chisel holder and protrudes from the latter. Normally, a narrow groove, into which a blockage in the form of a safety ring, a clamp or a splint is inserted, is assigned here to the end section of the shaft. Such solutions lead to difficulties, in as much as contamination collects between the shaft and the chisel holder hole and, due to friction wear, results in an ever increasing clearance at the inner hole. When the chisel holder hole has been expanded very much, the safety mechanism may also become ineffective, so that the chisel falls out of the chisel holder.
In a different U.S. Pat. No. 4,944,559, the groove is disposed at the shaft of the chisel, which protrudes from the hole of the chisel holder. In the case of this arrangement, there are sometimes even double safety mechanisms, predominantly in the form of two Seger rings or of one Seger ring and a locking barrier.
Starting out from this state of the art, it is an object of the invention to indicate a generic chisel and a safety mechanism preventing the chisel falling out during operation, which avoid the disadvantages of the previously known solutions, can be handled easily, have a simple structure and facilitate exchanging the chisel. The solution shall be usable equally for chisels, the shaft of which has a uniform diameter throughout its length, as well as for chisels, the shaft of which has a stepped diameter. The invention shall be suitable for fastening the chisel directly in the chisel holder as well as for fastening it in an intermediate sleeve.
Pursuant to the invention, this objective is accomplished owing to the fact that the end part of the chisel shaft is equipped with a projection, which is constructed as a lug and sloped to both sides, and that is, provided with chamfers. A friction ring, the diameter of which in the relaxed state is larger than the diameter of the hole of the chisel holder, is placed on the lug. At its upper and lower ends, the friction ring has inwardly inclined slopes, which are adapted to the chamfers of the lug. The chamfers of the lug and the slopes of the friction ring, inclined inwards on both side, cause of the friction ring to remain in the region of the lug during the insertion as well as during the expulsion of the chisel and prevent it from being pushed onto another part of the shaft. Because of this restricted guidance, there is no undesirable expansion of the friction ring. Moreover, in comparison with conventional shaft shapes with broad, smoothed accommodating grooves for a sleeve or a friction ring, the lug-shaped accommodating region of the shaft has the advantage for the friction ring that the lug does not represent an appreciable thinning of the material relative to the rest of the shaft and, in this respect, contributes, in addition to the rest of the shaft region, to the stabilization of the chisel during the rotation of the latter.
For the inventive solution, the effective fastening, as well as the easy, rapid and reliable handling during the fastening are of advantage. It also advantageous that a separate blocking piece does not have to be provided, since the friction ring is placed on the shaft of the chisel already by the manufacturer and is disposed of together with the worn out chisel. This construction of the safety mechanism for the chisel is not expensive and perhaps even less expensive than that of known safety mechanisms. Moreover, the inventive construction ensures and unimpeded rotation of the chisel in the chisel holder and, with that, a uniform wear. Since the lug is constructed as a simple extension of the shaft, the stability of the shaft, introduced into the chisel holder, is increased. The expansion of the chisel holder hole and the eventual breakage of the chisel, which are customary when chisels with short shafts are used, are avoided.
Further advantages of the invention arise out of the remaining dependent claims as well as from the following description of a preferred embodiment.